No. 4344-4/9

STK401-090

Description of External Circuits

C1, 11

For input coupling capacitor. Used for DC current blocking. When capacitor reactance with low

frequency is increased, the reactance value should be reduced in order to reduce the output

noise from the signal resistance dependent 1/f noise. In response to the popping noise which

occurs when the system power is turned on, C1 and C11 which determine the decay time

constant on the input side are increased while C3 and C13 on the NF side are decreased.

C2, 12

For input filter capacitor. Permits high-region noise reduction by utilizing filter constructed with

R1 and R11.

C3, 13

For NF capacitor. This capacitor determines the decline of the cut-off frequency and is

calculated according to the following equation.

1

2

π X C3 (13) X R3 (13)

For the purpose of achieving voltage gains prior to reduction, it is best that C3 and C13 are large.

However, because the shock noise which occurs when the system power is turned on tends to

increase, values larger than those absolutely necessary should be avoided.

C5, 15

For oscillation prevention capacitor. A Mylar capacitor with temperature and frequency features

is recommended.

C6, 7

For oscillation prevention capacitor. To ensure safe IC functioning, the capacitor should be

installed as close as possible to the IC power pin to reduce power impedance. An electrolytic

capacitor is good.

C8, 9

For decoupling capacitor. Reduces shock noise during power up using decay time constant

circuits with R8 and R9 and eliminates components such as ripples crossing over into the input

side from the power line.

R1, 11

For input filter applied resistor.

R2, 12

For input bias resistor. The input pin is biased to zero potential. Input impedance is mostly

decided with this resistance value.

R3, 13, 4, 14

For resistors to determine voltage gain (VG). We recommend a VG = 40 dB using R3 and R13 =

560

Ω and R4 and R14 = 56Ω. VG adjustments are best performed using R3 and R13. When

using R4 and R14 for such purposes, R4 and R14 should be set to equal R2 and R12 in order to

R5, 15

For oscillation prevention resistor.

R6, 16

For oscillation prevention resistor. This resistor’s electrical output resides in the signal frequency

and is calculated according to the following formula.

P R6 (16) =

(

√2

)

2

X R6 (16)

1/2

π fC5 (15) + R6 (16)

f = output signal frequency upper limit

R8, 9

according to this value. Set the electrical output of these resistors while keeping in mind the flow

of peak current during recharging to C8 and C9 which function as pre-drive TR control resistors

during load shorts.

L1, 2

For oscillation prevention coil. Compensates

phase dislocation caused by load capacitors

and ensures stable oscillation.